Sparking plug



Patented Feb. 15, 1938 PATENT GFFIQE SPARKING PLUG Charles Molyneux Carin gton and Archibald Edward Postlethwaite, London, England, assignors to K. L. G. Sparkin g Plugs Limited, London,

England, a British company Application July 7,

In Great Britain 10 Claims.

This invention is for improvements in sparking-plugs, for internal-combustion engines, of the kind in which the earthed electrode, which is carried by the body of the plug, is constituted by one or more fine wires; a sparking-plug of this kind is described in British patent specification No. 448,913.

The attachment of the wires to the body of the plug has hitherto presented serious manufacturing difficulties. For example, it is commercially impracticable to drill holes of, say, .02 inch diameter in the plug-body owing to the frequent breakage of the drill bits. The object of this invention is to provide an inexpensive mounting for the fine wires.

According to the present invention, the plugbody comprises two interengaging parts, and each wire is located by a groove in one part; preferably each groove is closed by the other part. The said grooves are preferably formed in the said part prior to the fitting of the parts together, and the width of each groove is preferably slightly less than the diameter of the wire, so that the wireis gripped in addition to being located, by the groove.

The part of the body which is formed with the grooves maybe a small metal ring which, when the wires have been inserted in the grooves, is placed on a shoulder in the plug-body which closes the grooves. The ring may be held in place by any suitable means.

Where the wires are disposed substantially radially with respect to the plug axis, they are located against movement radially outwards by their abutment against the inner wall of the plugbody surrounding the ring; in order to locate them against movement in the other direction each groove may be formed with a local enlargement at a part of its length other than its innerend so that the wire at this most end so that the diameter of the wire at this part is uncompressed, or is compressed to a less extent than the remainder, when the wire is forced into the groove. For example, the groove may be discontinued at a point near its outer point is undeformed and thus provides a head.

A specific embodiment of the present invention will now be described by way of example with reference to the accompanying drawing of which:-

Figure 1 is a plan view of the small metal ring into which the wires are afi'ixed,

Figure 2 is a sectional elevation on the line 2-2 of Figure 1,

Figure 3 is a diagram illustrating the method 1937, Serial No. 152,294

December 5, 1936 of inserting the wires into the grooves of the ring, Figure 4 being a sectional elevation to an enlarged scale on the line 4-4 of Figure 3 and Figure 5 a plan view, to the same enlarged scale, of the wire and the part of the ring shown in Figure 4, and

Figure 6 is a sectional elevation of the assembled sparking-plug body.

As shown first in Figures 1 and 2, a steel ring IE3 is milled on one face with six radial grooves H of substantially square cross-section. The outer edge of the grooved face of the ring is chamfered as shown at E2 and the inner edge of the other face is chamfered at IS. The purpose of these chamfers is explained below.

When the wires are to be inserted into the grooves, the ring I I] is placed on an anvil M having a locating ledge l5 and a central cylindrical mandrel Hi. The wires H1 are brought in from six supply spools until their ends abut against the mandrel E6 and they are then pressed lightly into the grooves H. A tubular tool E8 is now brought down on to the wires whereby they are pressed tightly into the grooves. An outer tool l9 slidable on the tube #8 is now pressed down so as to shear off the Wires flush with the outer wall of the ring ill.

The diameter of each wire is slightly greater than the corresponding dimension of the groove H. For example, the diameter of the wire may be .02 inch and each groove H may be .018 inch in breadth and .018 inch in depth. Consequently when the wires are forced into the grooves, the part of each wire which engages the groove is deformed into an approximately square shape as shown in Figure 4.

The friction between this deformed portion and the groove is sufiicient to retain the wire in position until the final assembly of the sparking-plug. The outer end of the wire, however, at the region of the chamfered edge I2 of the ring is unconstrained in a direction laterally of the groove so that at this region an enlarged head 23 is formed as shown in Figure 5 and in broken lines in Figure 4. This head is of larger transverse dimensions than the groove and therefore prevents movement of the wire in a direction towards the centre of the ring H1. The chamfer constitutes, in eifect, a local enlargement in the groove I! at the outer end of the groove. But such enlargement could be provided at any other part of the groove except at the innermost end thereof.

The pressure applied by the tool l8 may be such as to leave the wires standing very slightprovide with 1y above of the ring As shown in Figure In as shown in Figure 4. 6, the sparking-plug body 21 is formed near the mouth with an inwardlydirected shoulder 22. The ring with the wires in position is removed from the anvil l4, turned upsidedown, and placed with the wires downwards on the shoulder 22. The ring IE3 and the shoulder 22 thus constitute the two interengaging parts referred to above and in the claims. The upstanding wall 23 of the plug-body is now rolled down on to the ring Ill so as to clamp it tightly in position. In Figure 6 the wall '23 is shown on the left-hand side as it appears before the rolling operation and on the right-hand side as it appears after the rolling operation. The protrusion of each wire by a very small distance beyond the face of the ring ensures that, when the plug is finally assembled as above described, the wires are firmly clamped between the ring l0 and the shoulder 22.

In the assembled plug it will be seen that the wires II, the inner ends of which have been accurately positioned by their abutment against the mandrel iii, are prevented from moving radially outwards by the abutment of their outer ends against the wall of the plug-body. They are prevented from moving radially inwards by the enlarged heads described above with reference to Figures 4 and 5. Movement in any other direction is rendered impossible by the walls of the grooves and by the gripping action of the ring in and the shoulder 22.

The purpose of the inner chamfer I3 is to the rolled-over wall 23 of the body, a smooth entrance mouth to the plug, as shown on theright-hand side of Figure 6.

It will be understood that any desired number of wires may be used and that they need not be arranged radially. For example, each wire may pass continuously from one groove to another in either a straight or suitably curved path. The metal for the wire may be platinum, iridium, or platinum-iridium alloy.

We claim 1. A sparking-plug comprising a plug-body composed of two inter-engaging parts, one of which is grooved, and an electrode comprising at least one fine wire located in said groove.

2. A sparking-plug comprising a plug-body composed of two interengaging parts, one of which is formed with a plurality of grooves which are closed by the other part, and electrode means comprising a plurality of fine wires located by said grooves.

3. A sparking-plug comprising a body formed in two parts, one of which is formed with grooves prior to assembly of the plug, said grooves being closed by theother part, and electrode means comprising a plurality of fine wires located by said grooves.

4. A sparking-plug according to claim 3 wherein the width of each groove is such as to grip the wire within it.

5. A sparking-plug comprising a body, a metal ring adapted to engage the body and formed on one 'face with a plurality of radial grooves, a shoulder onthe'body against which the ring abuts so that the grooves are closed by the shoulder, and electrode means comprising fine wires located by said grooves.

6. A sparking-plug comprising a body having a shoulder, a metal ring'adapted to rest against said shoulder and formed with grooves which are closed by said shoulder, a rolled-over projection on the-body to locate said ring in position, and

electrode means comprising fine wires located by said grooves and said shoulder.

'7. A sparking-plug accordingto claim 6 whereineach said groove is formed with a local enlargement at a part of its length other than its innermost end.

8. A sparking-plugaccording to claim6 wherein each said groove is=discontinued at a point near its outer end.

9. A sparking-plug according to claim 6 wherein the grooved face of the ring is chamfered at its outer edge.

10. A- sparking-plug comprising a plug-body having a shouldered recess, a flat ring adapted to reston the said-shoulder and formed on the at its outer edge and with radial grooves of rectangular cross-section, platinum wires adapted to engage the grooves in such manner as partially to protrude beyond the grooved face of .40 face which abuts said shoulder with a chamfer 

